Several approaches have been used to enable light emitting diodes (LEDs) to generate white light. A first approach is to use a blue LED in combination with a yellow phosphor. A portion of the blue light from the LED is converted into yellow light by the phosphor. The yellow light mixes with residual blue light to form white light. A disadvantage of this approach is the conversion efficiency of the phosphor is about 60%, so the light source is not efficient.
A second approach is to use a combination of LEDs of different colors to produce white light. In this approach, two or three LED dies are located side by side. For example, a blue LED may be used with an amber LED. However, with this approach it is difficult to obtain the accurate color mixing required to form white light.